A wide variety of pneumatic fluid dispensers that dispense adhesives, sealants, lubricants and other fluids and liquids in a wide range of viscosities are well known. Pneumatic fluid dispensers have historically been favored because, in a manual dispenser, they are light and easy to manipulate, as well as relatively inexpensive to manufacture and operate. Further, pneumatic technology has continued to improve, so that pneumatic fluid dispensers continue to be widely used. However, applications requiring faster and more precise fluid dispensing in both manual and automated settings continue to grow rapidly. The requirements and specifications for fluid dispensing applications are ever more rigorous. Many applications require that fluids be dispensed in very precise volumes, at very precise locations and at fast cycle (on/off) rates.
Pneumatic fluid dispensers commonly utilize pressurized or “shop” air commonly found in a manufacturing environment. Using a manually initiated or automatically generated command signal, the pressurized air is typically directed against a piston in a syringe barrel holding a liquid. In other applications, the pressurized air may be directly applied to the liquid. The resulting force urges the liquid from the syringe. Pneumatic dispensers are known to use air flow regulators to control the pressurized air supplied to the barrel. Such regulators act as flow restrictors and extend the time required to fill the air space in the syringe barrel with the requisite air needed to reach a fully pressurized dispensing condition. In addition, vacuum generators on the exhaust side of the dispenser are used for purposes of placing the air space of the syringe barrel under vacuum to prevent dripping. These vacuum generators, which may be venturi devices, act as air flow restrictions on the exhaust side and lengthen the time for venting the syringe barrel when stopping a dispense cycle. The effect is an overall increase in the dispense cycle time that may be achieved, i.e., the time necessary to complete one full “on” to “off” cycle of liquid dispensing. Other aspects of typical dispensers that can increase cycle time include locating the pneumatic controls away from the dispensing syringe and directing the pressurized air through a tube coupled between a control unit and the dispensing syringe. The added air volume and restricting effect represented by the tube results in an increased pressurization time at the beginning of each dispense cycle.
It would be desirable to provide dispensing apparatus and methods that address these and other issues with existing apparatus and methods.